1. Field of Use
This disclosure is generally directed to fuser members useful in electrophotographic imaging apparatuses, including digital, image on image, and the like.
2. Background
In a typical electrophotographic imaging apparatus, an image of an original to be copied, or the electronic document image, is recorded in the form of an electrostatic latent image upon a photosensitive member and the latent image is subsequently rendered visible by the application of thermoplastic resin particles or composites thereof which are commonly referred to as toner. The visible toner image is in a loose powdered form and can be easily disturbed or destroyed. The toner image is usually fixed or fused upon a substrate or support member which may be a cut sheet or continuous media, such as plain paper.
The use of thermal energy for fixing toner images onto a support member is well known. In order to fuse toner material onto a support surface permanently by heat, it is necessary to elevate the temperature of the toner material to a point at which the constituents of the toner material coalesce and become tacky. This heating causes the toner to flow to some extent into the fibers or pores of the support member. Thereafter, as the toner material cools, solidification of the toner material causes the toner material to be firmly bonded to the support.
Several approaches to thermal fusing of toner images have been described in the prior art. These methods include providing the application of heat and pressure substantially concurrently by various means: a roll pair maintained in pressure contact; a belt member in pressure contact with a roll; and the like. Heat may be applied by heating one or both of the rolls, plate members or belt members. The fusing of the toner particles takes place when the proper combination of heat, pressure and contact time is provided. The balancing of these parameters to bring about the fusing of the toner particles is well known in the art, and they can be adjusted to suit particular machines or process conditions.
During operation of a fusing system in which heat is applied to cause thermal fusing of the toner particles onto a support, both the toner image and the support are passed through a nip formed between the roll pair, or plate or belt members. The concurrent transfer of heat and the application of pressure in the nip affect the fusing of the toner image onto the support. It is important in the fusing process that no offset of the toner particles from the support to the fuser member take place during normal operations. Toner particles that offset onto the fuser member may subsequently transfer to other parts of the machine or onto the support in subsequent copying cycles, thus increasing the background density or interfering with the material being copied there. The referred to “hot offset” occurs when the temperature of the toner is increased to a point where the toner particles liquefy and a splitting of the molten toner takes place during the fusing operation with a portion remaining on the fuser member. The hot offset temperature or degradation to the hot offset temperature is a measure of the release property of the fuser member, and accordingly it is desired to provide a fusing surface with a low surface energy to provide the necessary release.
A fuser or image fixing member, which can be a roll or a belt, may be prepared by applying one or more layers to a suitable substrate. Cylindrical fuser and fixer rolls, for example, may be prepared by applying an elastomer or fluoroelastomer to an aluminum cylinder. The coated roll is heated to cure the elastomer. Such processing is disclosed, for example, in U.S. Pat. Nos. 5,501,881, 5,512,409, and 5,729,813, the disclosure of each of which is incorporated by reference herein in its entirety.
Current fuser members may be composed of a resilient silicone layer with a fluoropolymer topcoat as the release layer. Fluoropolymers can withstand high temperature) (>200°) and pressure conditions and exhibit chemical stability and low surface energy, i.e. release properties. There are typically two types of fuser topcoat materials used for the current fuser member—fluoroelastomers and fluoroplastics. Fluoroelastomers have good mechanical flexibility, provide shock absorbing properties and typically require a release agent to prevent offset due to their higher surface energy. Fluoroplastics, such as TEFLON® from E.I. DuPont de Nemours, Inc. have a lower surface energy due to high fluorine content and are widely used for oil-less fusing. However, fluoroplastics typically lack mechanical flexibility, which can cause, for example, denting, cracking, and abrasion.
Semi-crystalline and certain thermosetting polymers, such as polyamides, polystyrene, polycarbonates, Teflon resins, phenol resins, epoxy-resins and the like, have been widely used as engineering materials in numerous applications. These materials, however, are generally prone to ductile failure due to their inherent brittleness. One of the most important and commonly applied strategies to improve the mechanical performance of semi-crystalline polymers is achieved by adding rubber fillers. It is theorized that sub-micron rubber fillers in polymer form cavitations around the filled rubber particles and thereby toughen the polymers. The cavitated rubber particles increase stress in the polymer matrix through plastic deformation. Thus, the hydrostatic pressure is relieved near the voids, and the stresses that cause fracture failure are redistributed in a crystalline material. Several models have been developed for polymer toughening mechanism. For fillers to be effective for toughening, the average inter-particle distance should be smaller than a critical length Lc, which is governed by the mean distance between micro-cracks and the average size of dispersed filler particles. Therefore, for a given polymer matrix, one possible way to reduce the critical rubber volume fraction for effective toughening is to decrease the filler particle size.
Although their fracture toughness can be significantly improved, the rubber-toughened polymers typically result in a dramatic drop in modulus. To overcome the drop in modulus fillers having a hard core and a soft-shell are added to the polymer matrix. Many approaches have been developed to create core-shell fillers for toughening semi-crystalline polymers. For instance, toughening with block copolymers has been widely used for many polymer systems. The challenge associated with this approach is that specific block copolymers need to be synthesized to control the morphology and domain sizes for different polymers.